Compositions for erosion and molten dust resistant environmental barrier coatings

ABSTRACT

Compounds are generally provided, which may be particularly used to form a layer in a coating system. In one embodiment, the compound may have the formula: A x B b Ln 1-x-b Hf 1-t-d Ti t D d MO 6 , where: A is Al, Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof; x is about 0.01 to about 0.99; b is 0 to about 0.5, with 1-x-b being 0 to about 0.99 such that Ln is present in the compound; Ln is a rare earth or a mixture thereof that is different than A; t is 0 to about 0.99; D is Zr, Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5; the sum of t and d is less than 1 such that Hf is present in the compound; and M is Ta, Nb, or a mixture thereof.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a divisional of U.S. patent application Ser. No.15/689,406 now U.S. Pat. No. 10,696,601, entitled “COMPOSITIONS FOREROSION AND MOLTEN DUST RESISTANT ENVIRONMENTAL BARRIER COATINGS”, filedAug. 29, 2017, which is incorporated herein by reference.

FIELD OF TECHNOLOGY

Embodiments of the present invention generally relate to environmentalbarrier coatings for ceramic components, along with methods of makingthe same.

BACKGROUND

Higher operating temperatures for gas turbine engines are continuouslybeing sought in order to improve their efficiency. However, as operatingtemperatures increase, the high temperature durability of the componentsof the engine must correspondingly increase. Significant advances inhigh temperature capabilities have been achieved through the formulationof iron, nickel, and cobalt-based superalloys. Still, with many hot gaspath components constructed from supper alloys, thermal barrier coatings(TBCs) can be utilized to insulate the components and can sustain anappreciable temperature difference between the load-bearing alloys andthe coating surface, thus limiting the thermal exposure of thestructural component.

While superalloys have found wide use for components used throughout gasturbine engines, and especially in the higher temperature sections,alternative lighter-weight substrate materials have been proposed, suchas ceramic matrix composite (CMC) materials. CMC and monolithic ceramiccomponents can be coated with environmental barrier coatings (EBCs) toprotect them from the harsh environment of high temperature enginesections. EBCs can provide a dense, hermetic seal against the corrosivegases in the hot combustion environment.

Silicon carbide and silicon nitride ceramics undergo oxidation in dry,high temperature environments. This oxidation produces a passive,silicon oxide scale on the surface of the material. In moist, hightemperature environments containing water vapor, such as a turbineengine, both oxidation and recession occurs due to the formation of apassive silicon oxide scale and subsequent conversion of the siliconoxide to gaseous silicon hydroxide, which results in dimensional loss ofthe material. For component applications of silicon-based substrates inturbine engines, such material loss can open up clearances and may leadto efficiency losses, and ultimately may lead to perforation of thecomponent.

As such, an environmental barrier coating (EBC) is applied onto thesurface of the ceramics to help protect the underlying component.Current materials commonly used for environmental barrier coatings onCMC's include celsian-phase barium strontium aluminosilicate (BSAS) andrare earth silicates. All of these materials are relatively stable insteam compared to the CMC and can prevent penetration of steam to theCMC if present as a dense coating layer.

However, these materials have varying resistance against moltenenvironmental contaminant compositions, particularly those containingoxides of calcium, magnesium, aluminum, silicon, and mixtures thereof.Dirt, ash, and dust ingested by gas turbine engines, for instance, areoften made up of such compounds, which often combine to form contaminantcompositions comprising mixed calcium-magnesium-aluminum-silicon-oxidesystems (Ca—Mg—Al—Si—O), hereafter referred to as “CMAS.” At the highturbine operating temperatures, these environmental contaminants canadhere to the hot barrier coating surface, and thus cause damage to theEBC. For example, CMAS can form compositions that are liquid or moltenat the operating temperatures of the turbines. The molten CMAScomposition can dissolve the barrier coating, or can fill its porousstructure by infiltrating the pores, channels, cracks, or other cavitiesin the coating. Upon cooling, the infiltrated CMAS compositionsolidifies and reduces the coating strain tolerance, thus initiating andpropagating cracks that may cause delamination and spalling of thecoating material.

In particular, molten dust reacts strongly with BSAS to form a lowtemperature eutectic and phases that are not stable in steam. Moltendust is less corrosive against rare earth silicates. Some rare earthsilicates (e.g. those comprised of gadolinium, erbium, and yttrium)react with the molten dust to form highly refractory “apatite” phases.Others rare earth silicates allow CMAS penetration but do not suffermelt point suppression. All rare earth silicates, however, aremechanically weakened by their interaction with molten dust, such thatsubsequent erosion and impact events can more easily take off thecoating.

A need exists, therefore, for coating compositions that are lesssusceptible to molten dust attack, and also less susceptible tosubsequent gas erosion, particle erosion, and particle impact over thecurrent state-of-the-art EBC materials.

BRIEF DESCRIPTION

Aspects and advantages will be set forth in part in the followingdescription, or may be obvious from the description, or may be learnedthrough practice of the invention.

Compounds are generally provided, which may be particularly used to forma layer in a coating system. In one embodiment, the compound may havethe formula:A_(x)B_(b)Ln_(1-x-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆where: A is Al, Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof; x is about0.01 to about 0.99; b is 0 to about 0.5, with 1-x-b being 0 to about0.99 such that Ln is present in the compound; Ln is Sc, Y, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof,and wherein Ln is different than A in terms of composition; t is 0 toabout 0.99; D is Zr, Ce, Ge, Si, or a mixture thereof; d is 0 to about0.5; the sum of t and d is less than 1 such that Hf is present in thecompound; and M is Ta, Nb, or a mixture thereof.

In one particular embodiment, the compound may be an aluminum containinghafnium tantalate having the formula:Al_(1-x-y)A′_(x)A″_(y)HfTaO₆where: A′ is Er, Sm, or a mixture thereof; x is about 0.3 to about 0.45;A″ is In, Ga, or a mixture thereof; y is about 0.15 to about 0.35; and(x+y) is about 0.5 to about 0.7.

In one particular embodiment, the compound may be an aluminum and erbiumcontaining hafnium tantalate having the formula:Al_(1-x-y)Er_(x)Ga_(y)HfTaO₆where: x is about 0.4 to about 0.6; y is 0 to about 0.4; and (x+y) isabout 0.5 to about 0.85.

These and other features, aspects and advantages will become betterunderstood with reference to the following description and appendedclaims. The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and, together with the description, serve to explain certainprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appended Figs.,in which:

FIG. 1 shows an exemplary coated component having a substrate with acoating system thereon

FIG. 2 shows an exemplary coated component having a substrate with acoating system thereon; and

FIG. 3 is a schematic cross-sectional view of a gas turbine engine whichmay include the coated component of FIG. 1 therein.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements of the present invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

In the present disclosure, when a layer is being described as “on” or“over” another layer or substrate, it is to be understood that thelayers can either be directly contacting each other or have anotherlayer or feature between the layers, unless expressly stated to thecontrary. Thus, these terms are simply describing the relative positionof the layers to each other and do not necessarily mean “on top of”since the relative position above or below depends upon the orientationof the device to the viewer.

Chemical elements are discussed in the present disclosure using theircommon chemical abbreviation, such as commonly found on a periodic tableof elements. For example, hydrogen is represented by its common chemicalabbreviation H; helium is represented by its common chemicalabbreviation He; and so forth. As used herein, “Ln” refers to a rareearth element or a mixture of rare earth elements. More specifically,the “Ln” refers to the rare earth elements of scandium (Sc), yttrium(Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), lutetium (Lu), or mixtures thereof.

Compositions are generally provided for use as part of an environmentalbarrier coating (EBC), along with methods of coating a component withsuch compositions. Additionally, coating systems are generally providedfor use as an EBC coated on a surface of a substrate, along with theremethods of formation and the resulting coated components.

Generally, the compositions described herein are less susceptible tomolten dust, erosion, impact, and/or mixed mode degradation mechanismsthan current EBC compositions. Thus, the compositions provided hereinmay result in a more robust EBC, compared to current-state-of-the-artEBC, that remains on the substrate material to protect it from recessionagainst water vapor in turbine engine environments. In summary, thesematerials exhibit better resistance against molten dust as compared toBSAS and rare earth silicate EBC materials, and may have higher hardnessthan BSAS and rare earth silicate materials, particular after exposureto molten dust (e.g., CMAS). Thus, the compound add resistance toparticle erosion and impact to a coating formed from such materials(e.g., an EBC).

Referring now to the drawings, FIG. 1 shows an exemplary coatedcomponent 100 with a substrate 102 having a coating system 106 thereon.Generally, the coating system 106 includes an optional bond coating 104on the surface 103 of the substrate and an EBC 108 on the optional bondcoating 104. In the embodiment shown, the bond coating 104 is directlyon the surface 103 without any layer therebetween. However, in otherembodiments, one or more layers can be positioned between the bondcoating 104, when present, and the surface 103. In other embodiments,the EBC 108 may be formed directly on the surface 103 of the substrate102.

The EBC 108 may include any combination of one or more layers 110 formedfrom materials selected from typical EBC or thermal barrier coating(“TBC”) layer chemistries, including but not limited to rare earthsilicates (e.g., mono-silicates and di-silicates), aluminosilicates(e.g., mullite, barium strontium aluminosilicate (BSAS), rare earthaluminosilicates, etc.), hafnia, zirconia, stabilized hafnia, stabilizedzirconia, rare earth hafnates, rare earth zirconates, rare earth galliumoxide, etc.

In accordance with one particular embodiment, at least one of the layers110 of the EBC 108 includes a compound having the formula:A_(1-b)B_(b)Z_(1-d)D_(d)MO₆  (Formula 1)where A is Al, Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof; b is 0 toabout 0.5 (e.g., 0 to about 0.2, such as greater than 0 to about 0.5 orabout 0.001 to about 0.2); Z is Hf, Ti, or a mixture thereof; D is Zr,Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5 (e.g., 0 to about0.2, such as about 0.001 to about 0.5 or about 0.001 to about 0.2); andM is Ta, Nb, or a mixture thereof. Compounds of Formula 1 may exhibitproperties that are similar or better than existing BSAS and rare earthsilicate materials in terms of stability in high temperature steam.Additionally, these materials may exhibit better resistance againstmolten dust as compared to BSAS and rare earth silicate EBC materials.Furthermore, these materials may have higher hardness than BSAS and rareearth silicate materials, particularly after exposure to molten dust.This results in the coating being more resistant to particle erosion andimpact.

Generally, the compound having the Formula 1 may have multiple phases inthe layer 110, such as an orthorhomibic phase (e.g., with Pbcn or Pnmaspace groups), a tetragonal phase (e.g., with P4₂/mnm), or a monoclinicphase (e.g., with P2/c). As such, these materials may have a structurethat is completely different (in terms of phase) than TBC layers formedfrom material containing hafnium oxides or zirconium oxides, whichtypically have the phase P21/c for monoclinic hafnia and monocliniczirconia, or the phase P4₂/nmc for tetragonal hafnia and zirconia, orthe cubic structure for hafnia and zirconia.

It is to be understood that the compound has distinct “sites” in itscomposition, with the “A site” being formed by A and/or B of Formula 1,the “Z site” being formed by Z and/or D of Formula 1, the “M site,” andthe oxygens.

In certain embodiment, the compound may include a single element in the“A site” such that b is 0 and A is of an element selected from the groupconsisting of Al, Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, and Bi. In one exemplary embodiment,when b is 0 and A is Al, the compound is: AlZ_(1-d)D_(d)MO₆ (e.g.,AlZMO₆ when d is 0, such as AlHfTaO₆). In another exemplary embodiment,when b is 0 and A is Y, the compound has the formula: YZ_(1-d)D_(d)MO₆(e.g., YZMO₆ when d is 0, such as YHfTaO₆). In still another exemplaryembodiment, when b is 0 and A is Er, the compound has the formula:ErZ_(1-d)D_(d)MO₆ (e.g., ErZMO₆ when d is 0, such as ErHfTaO₆).

The “A site” of the compound having Formula 1 includes, in oneparticular embodiment, aluminum (Al) in combination with another Aelement (e.g., Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof). Withoutwishing to be bound by any particular theory, it is believed that thepresence of Al in the compound increases the hardness of the coating. Incertain embodiments, Al is present in combination with another elementat the “A site” and then the compound can be described as having theformula:Al_(x)A_(1-x-b)B_(b)Z_(1-d)D_(d)MO₆  (Formula 2)where x is about 0.01 to about 0.99; A is Ga, In, Sc, Y, Ce, Pr, Nd, Pm,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixturethereof; b is 0 to about 0.5 (e.g., 0 to about 0.2, such as about 0.001to about 0.5 or about 0.001 to about 0.2); Z is Hf, Ti, or a mixturethereof; D is Zr, Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5(e.g., 0 to about 0.2, such as about 0.001 to about 0.5 or about 0.001to about 0.2); and M is Ta, Nb, or a mixture thereof. In certainembodiments, x is about 0.05 to about 0.9, such as about 0.1 to about0.75. In one particular embodiment, up to half of the element mixture atthe A site of the compound of Formula 1 may be Al (e.g., x is about 0.1to about 0.5 in the compound of Formula 2).

In addition to Al, the “A site” of the compound having Formula 1includes, in one particular embodiment, a combination of Al and gallium(Ga), with or without the presence of another A element (e.g., In, Sc,Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co,Mn, Bi, or a mixture thereof). Without wishing to be bound by anyparticular theory, it is believed that the presence of Ga in thecompound reduces the average ionic radius of at the A site, whichadjusts the coefficient of thermal expansion (CTE) of the layer 110.Thus, the amount of Ga in the compound may be used to control the CTE ofthe layer 110 to adjust it to be as close to the CTE of the adjacentlayers within the coating system 106 and/or the CTE of the substrate102.

When the compound includes Al and Ga in a portion of the “A site,” thenthe compound can be descried as having the formula:Al_(x)Ga_(y)A_(1-x-y-b)B_(b)Z_(1-d)D_(d)MO₆  (Formula 3)where x is about 0.01 to about 0.99 as described above with respect toFormula 2; y is about 0.01 to about 0.9; x+y is 1 or less; A is In, Sc,Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co,Mn, Bi, or a mixture thereof; b is 0 to about 0.5 (e.g., 0 to about 0.2,such as about 0.001 to about 0.5 or about 0.001 to about 0.2); Z is Hf,Ti, or a mixture thereof; D is Zr, Ce, Ge, Si, or a mixture thereof d is0 to about 0.5 (e.g., 0 to about 0.2, such as about 0.001 to about 0.5or about 0.001 to about 0.2); and M is Ta, Nb, or a mixture thereof.Another element may be present at the A site in the compound of Formula3 when x+y is less than 1 (i.e., x+y>1). In one particular embodiment,up to half of the element mixture at the A site of the compound ofFormula 1 may be Al (e.g., x is about 0.1 to about 0.5 in the compoundof Formula 3) and up to half of the element mixture at the A site of thecompound of Formula 1 may be Ga (e.g., y is about 0.1 to about 0.5 inthe compound of Formula 3).

In particular embodiments, erbium (Er), yttrium (Y), and/or holmium (Ho)may be included within the A site of the compounds having the Formula 1,Formula 2, and/or Formula 3 (i.e., A includes Er, Y, Ho, or a mixturethereof in any of Formulas 1, 2, or 3). Without wishing to be bound byany particular theory, it is believed that the Er, Y, and/or Ho mayprovide CMAS resistance to the layer 110 formed from such a compound.

Referring to Formulas 1-3 where b is greater than 0, boron (B) dopes the“A site” of the compound of Formula 1 to change the CTE and/or thesintering temperature of the layer formed from the compound.Additionally, B may migrate to other layers (e.g., the bond coatingand/or thermally growth oxide layer) to help those layers interact withCMAS and/or to control the crystalition of those layers. However, inother embodiments, b is 0 such that no B is present in the compound.

The “Z site” of any of the compounds having Formula 1, 2, or 3 may beutilized, in one particular embodiment, to help control the CTE of thecompound. Generally, the CTE of the compound is directly proportional tothe ionic radius of at Z site. For example, the CTE of the compounddecreases as the ionic radius of the Z site element decreases. Inparticular embodiments, the Z site may include Hf, Ti, or a mixturethereof, such as represented in Formula 4:A_(1-b)B_(b)Hf_(h)Ti_(t)D_(1-h-t)MO₆  (Formula 4)where his 0 to 1, t is 0 to 1, and h+t is greater than 0 to 1; A is Al,Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,Fe, Cr, Co, Mn, Bi, or a mixture thereof; b is 0 to about 0.5 (e.g., 0to about 0.2, such as about 0.001 to about 0.5 or about 0.001 to about0.2); D is Zr, Ce, Ge, Si, or a mixture thereof; and M is Ta, Nb, or amixture thereof. In one particular embodiment of Formula 4, the A sitemay include Al (e.g., as discussed above with respect to Formula 2), Ga(e.g., as discussed above with respect to Formula 3), and/or othermaterials, and/or B (e.g., as discussed above with respect to Formulas1, 2, or 3). In certain embodiments, h+t may be greater than 0 but lessthan 1, such that another element (D) is present at the Z site.

In one embodiment, Hf is present in the compound such that h is greaterthan 0 to 1 (e.g., about 0.05 to about 1). In one particular embodimentwhen both Hf and Ti are present in the compound (i.e., both h and t aregreater than 0), Hf may be present in a molar amount that is greaterthan the amount of Ti, such that h is greater than t. In one embodiment,Hf may be the majority of the element in terms of molar ration (i.e., his 0.5 to 1) at the Z site. For example, h may be 1 in particularembodiments, such that t is 0 and 1-t is 0 (i.e., Hf is the sole elementat the Z site). Without wishing to be bound by any particular theory, itis believed that Hf in the Z site may increase hardness and the steamresistance of the coating formed from such a compound.

In particular embodiments, where Hf is present in the “Z site” (i.e., Zincludes Hf either alone or in combination with Ti and/or D), acombination of elements may be included in the “A site.” For example,such a compound may have the formula:A_(x)B_(b)Ln_(1-x-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆  (Formula 5)where: A is Al, Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof; x is about0.01 to about 0.99; b is 0 to about 0.5 with 1-x-b being 0 to about 0.99such that Ln is present in the compound; Ln is Sc, Y, La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof, andwith Ln being different than A in terms of composition; t is 0 to about0.99; D is Zr, Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5;the sum of t and d is less than 1 such that Hf is present in thecompound; and M is Ta, Nb, or a mixture thereof.

When A includes Al in combination with another element, Formula 5 can bemodified as follows:Al_(x)A′_(a)B_(b)Ln_(1-x-a-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆  (Formula 6)where: x is about 0.01 to about 0.99 such that Al is present in thecompound; A′ is Ga, In, Sc, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, Lu, Fe, Cr, Co, Mn, Bi, or a mixture thereof; a is 0 toabout 0.99; b is 0 to about 0.5, with 1-x-a-b being 0 to about 0.99 suchthat Ln is present in the compound; Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof, and wherein Lnis different than A in terms of composition; t is 0 to about 0.99; D isZr, Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5; the sum of tand d is less than 1 such that Hf is present in the compound; and M isTa, Nb, or a mixture thereof.

For example, both Al and Ga may be present at the A site in combinationwith another element (with Hf included in the Z site), such as in theformula:Al_(x)Ga_(y)B_(b)Ln_(1-x-y-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆  (Formula 7)where: x is about 0.01 to about 0.99 such that Al is present in thecompound; y is about 0.01 to about 0.99 such that Ga is present in thecompound; b is 0 to about 0.5, with 1-x-a-b being 0 to about 0.99 suchthat Ln is present in the compound; Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof, and wherein Lnis different than A in terms of composition; t is 0 to about 0.99; D isZr, Ce, Ge, Si, or a mixture thereof d is 0 to about 0.5; the sum of tand d is less than 1 such that Hf is present in the compound; and M isTa, Nb, or a mixture thereof.

The material of the “M site” of the compound of any of Formulas 1-7 mayinfluence the phase allowance and CTE of the resulting compound. In oneparticular embodiment, the M site may be Nb without any additionalelement present, which may provide better phase allowance and CTEmatching when utilized as a layer within an EBC coating.

As stated, the compound of any of Formulas 1-7 may be included in alayer of an EBC 108 of the coating system 106 so as to provide amaterial having minimal reaction with CMAS and has high hardness (e.g.,for erosion resistance) after reaction with CMAS. Thus, the material ofthe compounds of any of Formulas 1-7 may be included within a layer ofthe EBC with other materials of an EBC layer, or may be used to form aseparate layer within the EBC 108. In one embodiment, a layer of the EBC108 is formed from the compound of any of Formulas 1-7, and may have athickness of about 1 μm to about 1 mm (e.g., 1 μm to about 100 μm).

In one embodiment, the compound of any of Formulas 1-7 may be includedin an outermost layer of an EBC 108 of the coating system 106, such thatthe compound may help protect the underlying EBC layers and substrate102. The substrate 102 may be formed from a ceramic matrix composite(“CMC”) material, such as a silicon based, non-oxide ceramic matrixcomposite. As used herein, “CMC” refers to a silicon-containing, oroxide-oxide, matrix and reinforcing material. As used herein,“monolithic ceramics” refers to materials without fiber reinforcement(e.g., having the matrix material only). Herein, CMCs and monolithicceramics are collectively referred to as “ceramics.”

Some examples of CMCs acceptable for use herein can include, but are notlimited to, materials having a matrix and reinforcing fibers comprisingnon-oxide silicon-based materials such as silicon carbide, siliconnitride, silicon oxycarbides, silicon oxynitrides, and mixtures thereof.Examples include, but are not limited to, CMCs with silicon carbidematrix and silicon carbide fiber; silicon nitride matrix and siliconcarbide fiber; and silicon carbide/silicon nitride matrix mixture andsilicon carbide fiber. Furthermore, CMCs can have a matrix andreinforcing fibers comprised of oxide ceramics. Specifically, theoxide-oxide CMCs may be comprised of a matrix and reinforcing fiberscomprising oxide-based materials such as aluminum oxide (Al₂O₃), silicondioxide (SiO₂), aluminosilicates, and mixtures thereof. Aluminosilicatescan include crystalline materials such as mullite (3Al₂O₃ 2SiO₂), aswell as glassy aluminosilicates.

Particularly suitable compounds for use as a relatively thick or thinEBC layer may have a particularly close coefficient of thermal expansion(CTE) to the underlying CMC substrate. For example, aluminum containinghafnium tantalates may be particularly suitable compounds having CTEsrelatively close to that of the CMC substrate. For example, aluminumcontaining hafnium tantalates may have the formula:Al_(1-x-y)A′_(x)A″_(y)HfTaO₆  (Formula 8)where A′ is Er, Sm, or a mixture thereof; x is about 0.3 to about 0.45;A″ is In, Ga, or a mixture thereof; y is about 0.15 to about 0.35; and(x+y) is about 0.5 to about 0.7 such that Al is present from about 0.3to about 0.5. In particular embodiments, A′ is either Er or Sm, and/orA″ is either In or Ga. The compound of Formula 8 may also be referringto from Formula 1 where (referring to Formula 1) A includes Al incombination with two other elements (A′ and A″ of Formula 8); b is 0, Zis Hf, d is 0, and M is Ta.

Particularly suitable compounds for use as a relatively thin EBC layer(e.g. having a thickness of about 100 μm or less) may have a coefficientof thermal expansion (CTE) that is close to the CTE of the underlyingCMC substrate but not within a CTE matching relations. For example,erbium containing hafnium tantalates may be particularly suitablecompounds for such EBC layers, and may have the formula:Al_(1-x-y)Er_(x)Ga_(y)HfTaO₆  (Formula 9)where x is about 0.4 to about 0.6; y is 0 to about 0.4; and (x+y) isabout 0.5 to about 0.85 such that Al is present from about 0.15 to about0.5. The compound of Formula 9 may also be referring to from Formula 1where (referring to Formula 1) A includes a combination of Er, Al, andGa; b is 0, Z is Hf, d is 0, and M is Ta.

As shown, the bond coating 104 is optionally positioned on the surface103 of the substrate 102 between the substrate 102 and the EBC 108. Whenpresent, the bond coating 104 includes silicon or a silicon basedmaterial (e.g., a silicide, etc.). Generally, the bond coating 104 isrelatively thin, such as having a thickness that is about 25 micrometers(μm) to about 275 μm, such as about 25 μm to about 150 μm (e.g., about25 μm to about 100).

FIG. 2 shows a thermally grown oxide (“TGO”) layer 105, which may formon the surface of the silicon-based bond coating 104, such as a layer ofsilicon oxide (sometimes referred to as “silicon oxide scale” or “silicascale”), during exposure to oxygen (e.g., during manufacturing and/oruse) of the component 100.

The coated component 100 of FIG. 1 is particularly suitable for use as acomponent found in high temperature environments, such as those presentin gas turbine engines, for example, combustor components, turbineblades, shrouds, nozzles, heat shields, and vanes. In particular, theturbine component can be a CMC component positioned within a hot gasflow path of the gas turbine such that the coating system 106 forms anenvironmental barrier for the underlying substrate 102 to protect thecomponent 100 within the gas turbine when exposed to the hot gas flowpath.

FIG. 3 is a schematic cross-sectional view of a gas turbine engine inaccordance with an exemplary embodiment of the present disclosure. Moreparticularly, for the embodiment of FIG. 3 , the gas turbine engine is ahigh-bypass turbofan jet engine 10, referred to herein as “turbofanengine 10.” As shown in FIG. 3 , the turbofan engine 10 defines an axialdirection A (extending parallel to a longitudinal centerline 12 providedfor reference) and a radial direction R. In general, the turbofan 10includes a fan section 14 and a core turbine engine 16 disposeddownstream from the fan section 14. Although described below withreference to a turbofan engine 10, the present disclosure is applicableto turbomachinery in general, including turbojet, turboprop andturboshaft gas turbine engines, including industrial and marine gasturbine engines and auxiliary power units.

The exemplary core turbine engine 16 depicted generally includes asubstantially tubular outer casing 18 that defines an annular inlet 20.The outer casing 18 encases, in serial flow relationship, a compressorsection including a booster or low pressure (LP) compressor 22 and ahigh pressure (HP) compressor 24; a combustion section 26; a turbinesection including a high pressure (HP) turbine 28 and a low pressure(LP) turbine 30; and a jet exhaust nozzle section 32. A high pressure(HP) shaft or spool 34 drivingly connects the HP turbine 28 to the HPcompressor 24. A low pressure (LP) shaft or spool 36 drivingly connectsthe LP turbine 30 to the LP compressor 22.

For the embodiment depicted, the fan section 14 includes a variablepitch fan 38 having a plurality of fan blades 40 coupled to a disk 42 ina spaced apart manner. As depicted, the fan blades 40 extend outwardlyfrom disk 42 generally along the radial direction R. Each fan blade 40is rotatable relative to the disk 42 about a pitch axis P by virtue ofthe fan blades 40 being operatively coupled to a suitable actuationmember 44 configured to collectively vary the pitch of the fan blades 40in unison. The fan blades 40, disk 42, and actuation member 44 aretogether rotatable about the longitudinal axis 12 by LP shaft 36 acrossan optional power gear box 46. The power gear box 46 includes aplurality of gears for stepping down the rotational speed of the LPshaft 36 to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of FIG. 3 , the disk 42 iscovered by rotatable front nacelle 48 aerodynamically contoured topromote an airflow through the plurality of fan blades 40. Additionally,the exemplary fan section 14 includes an annular fan casing or outernacelle 50 that circumferentially surrounds the fan 38 and/or at least aportion of the core turbine engine 16. It should be appreciated that thenacelle 50 may be configured to be supported relative to the coreturbine engine 16 by a plurality of circumferentially-spaced outletguide vanes 52. Moreover, a downstream section 54 of the nacelle 50 mayextend over an outer portion of the core turbine engine 16 so as todefine a bypass airflow passage 56 therebetween.

During operation of the turbofan engine 10, a volume of air 58 entersthe turbofan 10 through an associated inlet 60 of the nacelle 50 and/orfan section 14. As the volume of air 58 passes across the fan blades 40,a first portion of the air 58 as indicated by arrows 62 is directed orrouted into the bypass airflow passage 56 and a second portion of theair 58 as indicated by arrow 64 is directed or routed into the LPcompressor 22. The ratio between the first portion of air 62 and thesecond portion of air 64 is commonly known as a bypass ratio. Thepressure of the second portion of air 64 is then increased as it isrouted through the high pressure (HP) compressor 24 and into thecombustion section 26, where it is mixed with fuel and burned to providecombustion gases 66.

The combustion gases 66 are routed through the HP turbine 28 where aportion of thermal and/or kinetic energy from the combustion gases 66 isextracted via sequential stages of HP turbine stator vanes 68 that arecoupled to the outer casing 18 and HP turbine rotor blades 70 that arecoupled to the HP shaft or spool 34, thus causing the HP shaft or spool34 to rotate, thereby supporting operation of the HP compressor 24. Thecombustion gases 66 are then routed through the LP turbine 30 where asecond portion of thermal and kinetic energy is extracted from thecombustion gases 66 via sequential stages of LP turbine stator vanes 72that are coupled to the outer casing 18 and LP turbine rotor blades 74that are coupled to the LP shaft or spool 36, thus causing the LP shaftor spool 36 to rotate, thereby supporting operation of the LP compressor22 and/or rotation of the fan 38.

The combustion gases 66 are subsequently routed through the jet exhaustnozzle section 32 of the core turbine engine 16 to provide propulsivethrust. Simultaneously, the pressure of the first portion of air 62 issubstantially increased as the first portion of air 62 is routed throughthe bypass airflow passage 56 before it is exhausted from a fan nozzleexhaust section 76 of the turbofan 10, also providing propulsive thrust.The HP turbine 28, the LP turbine 30, and the jet exhaust nozzle section32 at least partially define a hot gas path 78 for routing thecombustion gases 66 through the core turbine engine 16.

Example 1

Aluminum containing hafnium tantalates, according to Formula 8, wheremade according to the formulas shown in Table 1. Each of these aluminumcontaining hafnium tantalate compounds had a CTE that was close to theCTE of a CMC substrate, making these compounds particularly suitable foruse as a layer of a EBC coating system.

TABLE 1 Compound CTE (×10⁻⁶/° F.) Er_(0.33)Al_(0.37)In_(0.3)HfTaO₆ 2.70Sm_(0.43)Al_(0.4)Ga_(0.17)HfTaO₆ 1.98 Sm_(0.29)Al_(0.42)In_(0.29)HfTaO₆1.81 Sm_(0.36)Al_(0.47)In_(0.17)HfTaO₆ 2.15

Example 2

Aluminum containing hafnium tantalates, according to Formula 9, wheremade according to the formulas shown in Table 2. Each of these aluminumcontaining hafnium tantalate compounds had a CTE that, while not beingparticularly close to the CTE of a CMC substrate, was still suitable foruse as a thin layer of a EBC coating system.

TABLE 2 Compound CTE (×10⁻⁶/° F.) Er_(0.48)Al_(0.2)Ga_(0.32)HfTaO₆ 3.88Er_(0.557)Al_(0.443)HfTaO₆ 3.60

This written description uses exemplary embodiments to disclose theinvention, including the best mode, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyinclude structural elements that do not differ from the literal languageof the claims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. A compound having the formula:A_(x)B_(b)Ln_(1-x-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆ where: A is Al, Ga, In, Sc,Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co,Mn, Bi, or a mixture thereof; x is about 0.01 to about 0.99; b is 0 toabout 0.5, with 1-x-b being greater than 0 to about 0.99 such that Ln ispresent in the compound; Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu, or a mixture thereof, and wherein Ln isdifferent than A in terms of composition; t is 0 to about 0.99; D is Zr,Ce, Ge, Si, or a mixture thereof; d is 0 to about 0.5; the sum of t andd is less than 1 such that Hf is present in the compound; and M is Ta,Nb, or a mixture thereof.
 2. The compound of claim 1, wherein b is 0,and wherein x is about 0.05 to about 0.9.
 3. The compound of claim 1,wherein b is greater than 0 to about 0.5, and wherein x is about 0.05 toabout 0.9 with the sum of x and b being less than
 1. 4. The compound ofclaim 1, wherein b is 0, and wherein t is
 0. 5. The compound of claim 1,wherein b is 0, and wherein d is
 0. 6. The compound of claim 1, where: bis 0; t is 0; and d is
 0. 7. The compound of claim 6, where: M is Ta. 8.The compound of claim 1, where: M is Ta.
 9. The compound of claim 1,where: M is Nb.
 10. The compound of claim 1, where: M is a mixture of Taand Nb.
 11. The compound of claim 1, wherein A includes Al such that thecompound has the formula:A_(x)B_(b)Ln_(1-x-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆ where: x is about 0.01 toabout 0.99 such that Al is present in the compound; A′ is Ga, In, Sc, Y,Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Fe, Cr, Co, Mn,Bi, or a mixture thereof; a is 0 to about 0.99; b is 0 to about 0.5,with 1-x-a-b being greater than 0 to about 0.99 such that Ln is presentin the compound; Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb, Lu, or a mixture thereof, and wherein Ln is differentthan A in terms of composition; t is 0 to about 0.99; D is Zr, Ce, Ge,Si, or a mixture thereof; d is 0 to about 0.5; the sum of t and d isless than 1 such that Hf is present in the compound; and M is Ta, Nb, ora mixture thereof.
 12. The compound of claim 11, where: M is Ta.
 13. Thecompound of claim 11, where: M is Nb.
 14. The compound of claim 11,where: M is a mixture of Ta and Nb.
 15. The compound of claim 1, whereinthe compound has the formulaA_(x)B_(b)Ln_(1-x-b)Hf_(1-t-d)Ti_(t)D_(d)MO₆ where: x is about 0.01 toabout 0.99 such that Al is present in the compound; y is about 0.01 toabout 0.99 such that Ga is present in the compound; b is 0 to about 0.5,with 1-x-a-b being greater than 0 to about 0.99 such that Ln is presentin the compound; Ln is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb, Lu, or a mixture thereof, and wherein Ln is differentthan A in terms of composition; t is 0 to about 0.99; D is Zr, Ce, Ge,Si, or a mixture thereof; d is 0 to about 0.5; the sum of t and d isless than 1 such that Hf is present in the compound; and M is Ta, Nb, ora mixture thereof.
 16. The compound of claim 15, where: M is Ta.
 17. Thecompound of claim 15, where: M is Nb.
 18. The compound of claim 15,where: M is a mixture of Ta and Nb.
 19. The compound as in claim 1,where Ln is Er, Y, Ho, or a mixture thereof.
 20. The compound of claim1, wherein t is 0, and wherein d is greater than 0 to about 0.25.